Seberged is an island off the coast of Southern Egypt and though
its only small, it is a very interesting place in terms of
history, geology and biology. In recent times it is well known among divers, which come here to experience the thrill of a "bottomless" reef face at the outer margin of the island. But Seberged has much more to offer.
The Red Sea is a prime example for the tectonic breaking up of continents,
resulting in a long and narrow ocean. But despite the predominant extension
tectonics involved in the process of a continental break up, we often get also -
apparently paradoxically - compressional elements of tectonics in these zones.
In the case of Seberged the compression was extremely strong and resulted
in a massive upthrusting of mantle material to the surface of the earth and in
the formation of two islands : Seberged and neighbouring Shark Island in the ocean.
Hence the island of Seberged has a very complex geology with large slabs of mantle
derived rocks, consisting predominantly of fresh peridotites, which may
form lustrous green gemmy crystals up to 10 cm and more. The
ancient egypts and greeks knew about these peridote crystals, and mined them
for many centuries and the island became famous under the name of 'Topazios'
in the ancient world. Later in christian times the name changed to 'St.
Johns Island' before the island became forgotten for many a century.
The small island of Seberged was rediscovered in the 19th century,
when geologists explored the old mines and found interesting nickel deposits,
which were later mined in the Nasser era around 1960. Later the diving community discovered Seberged
and the beautiful reefs around the island, steeply rising 500 m out of the oceans depth.
And the modern geologist
became aware of the unique geology on the island which allow a rare opportunity
to investigate fresh and unweathered mantle derived rocks.
I had the privilege to have a short visit to remote Seberged in 1994. We
visited the remains of the ancient mines and admired the beauty of the
turquoise lagoon surrounding the island. Of course we also looked for peridote.
We found some small gemmy crystals, mere leftovers of century long mining, but we also
saw large - unfortunately not gemmy - olivine crystals embedded in peridotite
rock with about 1 m size. The crystals are typical "olive" green and display
a prismatic habitus. They seldom show idiomorphic crystal faces, but are
clearly individual crystals of remarkable dimensions. Pitty, that I didnt
took any photos of the crystals...
Update March 2007 : In our library you find a new link to an expedition report to Seberged in 1980, written by Peter Bancroft and published 1984 in his famous book "Gem & Crystal Treasures". Please click here for the report.